WO3/TiO2 composite coatings on titanium: A comprehensive review of fabrication strategies and structure/property/performance correlations in visible-light photocatalysis

Visible-light-driven photocatalysis continues to face major limitations due to insufficient light absorption and rapid charge recombination in conventional TiO2-based systems. Integrating WO3 with TiO2 has emerged as a promising strategy to overcome these constraints by enhancing visible-light responsiveness and improving charge carrier dynamics. Accordingly, this review addresses the central research question: How do different fabrication routes of WO3/TiO2 composite coatings influence their structural features and, consequently, their photocatalytic performance under visible light? The review critically surveys recent studies on the manufacture of WO3/TiO2 composite coatings, with a special focus on how different preparation processes such as sol–gel, anodizing, plasma electrolytic oxidation (PEO), and hybrid routes affect their structures, optical properties, and photocatalytic activities. The formation of effective WO3/TiO2 heterojunctions improves carrier separation and extends light absorption, leading to significant degradation of organic pollutants or enhanced water-splitting performance. Particular attention is given to the role of morphological parameters, such as porosity, surface area, crystalline phase composition, and nanoparticle dispersion, in dictating photocatalytic activity. A comparative summary of structure–property–performance correlations is provided through examination of a broad range of experimental studies. It outlines the challenges that now exist in optimizing WO3/TiO2 systems in real-world environmental and energy applications. The findings presented here form the basis for rationalizing next-generation visible-light-responsive photocatalysts.